In a separator of this type, the material to be graded and the air stream can introduced separately inside the space with an annular section defined by the guide blades and the rotor, or the material to be graded can be placed in suspension in the air stream before the latter is admitted into the space, through the blades. The air stream then penetrates the rotor and is evacuated via the output orifice.
In both cases, the air stream and the material to be graded are subjected to rotation, about the axis of the rotor, in the space with an annular section contained between the rotor and the guide blades. The particles forming the coarse section of the material are projected by the centrifugal force generated by this rotation against the guide blades and drop through the effect of gravity into a collecting hopper provided with an evacuation orifice, while the particles forming the fine fraction are entrained by the air stream through the rotor and the central output orifice.
The fine fraction that is separated contains practically all the particles the size of which is smaller than a first dimension, while the coarse fraction contains practically all the particles the size of which is larger than a second dimension, which is larger than the first one. In addition, the two fractions contain particles the size of which is between the first and second dimensions. This is reflected by a distribution curve comprising two substantially horizontal portions linked by an inclined portion the slope of which characterizes the separator.
The distribution of the particles of intermediate size in one or the other of the fractions characterizes the cut-off precision of the separator. In general, it is attempted to obtain, by construction, a cut-off that is as marked as possible between the two fractions, that is to say to reduce the interval between the first and second dimensions, which is reflected by a distribution curve with a steep slope.
In certain cases, the product that it is sought to be obtained has to have a grain size distribution that differs from that of the fraction, whether fine or coarse, obtained by means of a separator of this type. This applies particularly to cement obtained by compression grinding the clinker. Hitherto, the only solution to this problem was to use two separators placed in series or in parallel and adjusted to the different cut-off dimensions. This represents a costly solution.
The object of the present invention is to perfect separators of the type concerned so that it is possible to adjust the slope of the distribution curve in a simple manner, that is to say to modify the grain size distribution of the particles the size of which is between the first and second dimensions.